Talks resumed, however, and Kim dispatched an envoy - his spy chief Kim Yong-chol - to Washington on Friday to deliver a letter to Trump.
North Korea defends its nuclear and missile programs as a deterrent against what it sees as USA aggression.
The post came just around a day after Sanders confirmed that the two leaders had agreed on the time of their first meeting. "I'll give whatever support is needed to my friends, President Trump and Marshall Kim Jong Un", he wrote.
"They're very powerful, and we would not take those sanctions off unless North Korea denuclearises", she said.
Both leaders are under pressure to get something out of the summit that is drawing global media scrutiny, with Kim seeking ways to reduce economic sanctions on his impoverished country.
The North may want to send a large delegation to accompany Mr Kim and provide its own security.
"A lot of times in situations that involve complex diplomacy, countries like to identify ambassadors of goodwill", a source said.
The summit holds great importance as the denuclearisation of North Korea is expected to be discussed.
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"I'd be cautious about saying the leadership shuffle is a sign of Kim's weakness", Jung Pak, a senior fellow at the Brookings Institution and a former deputy national intelligence officer in the Office of the Director of National Intelligence.
In keeping with normal practice, Singapore, as the host nation, will have to pay out for general security and various other expenses.
Japanese Prime Minister Shinzo Abe would be at the White House later this week for talks with Trump on the latter's summit meeting with North Korea.
A coup attempt "hasn't happened because there are competing security services that report not only on citizens, but on each other", said Klingner, a former Central Intelligence Agency deputy division chief for Korea.
"It wouldn't be my style to have to ask the US for help on the abduction issue", said Hitoshi Tanaka, a former diplomat and head of a think tank, the Institute for International Strategy. We can go fast. "We're going to start a process".
When it comes to paying for lodging at North Korea's preferred five-star luxury hotel, the United States is open to covering the costs, the two people said, but it's mindful that Pyongyang may view a USA payment as insulting.
The softening of Trump's rhetoric was more palpable after he received North Korean leader Kim Jong-un's special envoy at the White House last week.